DESCRIPTION (From the Applicant's Abstract): In the brains of mammals, birds and invertebrates, the sensory world is organized into regular neuronal arrays or maps. Common examples are the map of body surface in somatosensory cortex (the so called "homunculus") and the representation of oriented bars or edges in visual cortex. In these maps, neighboring cells respond to similar features of stimuli in the sensory periphery, and there is usually an orderly progression of the optimal stimulus across the array of neurons. Through the efforts of Hubel, Wiesel and many of their colleagues we now have a fairly comprehensive description of maps of stimulus preference in many areas of cortex, but fundamental questions regarding their development of function remain unanswered despite more that forty years of intense research. Sensory maps in the cortex are established by the orderly arrangement of afferents from the thalamus to layer IV in the cortex. The precise development of these maps requires, at least in part, afferent neuronal activity, and is subject to use-dependent modification that relies on the sensory experience of the animal. The objectives of the research outlined in this proposal are: (1) determine the cellular and synaptic features of the development of thalamocortical connections in mice with normal sensory experience; (2) determine the influence of sensory experience and neuronal activity on the development of thalamocortical synapses; and (3) establish the cellular and synaptic mechanisms for sensory map plasticity at thalamocortical synapses in developing animals. Experiments addressing these questions will be performed in vitro with whole cell patch-clamp techniques from mouse somatosensory cortex using a thalamocortical brain slice preparation.